6^-18*6^42/6^20

To solve this expression, we can use the properties of exponents.

First, let's simplify the numerator: 6^-18 * 6^42

Using the rule that says "When multiplying two numbers with the same base, add the exponents," we can rewrite this as: 6^(-18 + 42)

Simplifying the exponent, we get: 6^24

Now, let's simplify the denominator: 6^20

Now we can put the expression back together by dividing the numerator by the denominator: 6^24 / 6^20

Using the rule that says "When dividing two numbers with the same base, subtract the exponents," we can rewrite this as: 6^(24 - 20)

Simplifying the exponent, we get: 6^4

Therefore, the final answer is 6^4.